Helen Gurley Brown, who as the author of “Sex and the Single Girl” shocked early-1960s America with the news that unmarried women not only had sex but thoroughly enjoyed it — and who as the editor of Cosmopolitan magazine spent the next three decades telling those women precisely how to enjoy it even more — died on Monday in Manhattan. She was 90, though parts of her were considerably younger.

The Hearst Corporation, Cosmopolitan’s publisher, said in a news release that she died at NewYork-Presbyterian/Columbia hospital after a brief stay there. She lived in Manhattan.

As Cosmopolitan’s editor from 1965 until 1997, Ms. Brown was widely credited with being the first to introduce frank discussions of sex into magazines for women. The look of women’s magazines today — a sea of voluptuous models and titillating cover lines — is due in no small part to her influence.

Before she arrived at Cosmopolitan, Ms. Brown had already shaken the collective consciousness with her best-selling book “Sex and the Single Girl.” Published in 1962, the year before Betty Friedan ignited the modern women’s movement with “The Feminine Mystique,” it taught unmarried women how to look their best, have delicious affairs and ultimately bag a man for keeps, all in breathless, aphoristic prose. (Ms. Brown was a former advertising copywriter.)

By turns celebrated and castigated, Ms. Brown was for decades a highly visible, though barely visible, public presence. A tiny, fragile-looking woman who favored big jewelry, fishnet stockings and minidresses till she was well into her 80s, she was a regular guest at society soirees and appeared often on television. At 5 feet 4, she remained a wraithlike hundred pounds throughout her adult life. That weight, she often said, was five pounds above her ideal.

Ms. Brown routinely described herself as a feminist, but whether her work helped or hindered the cause of women’s liberation has been publicly debated for decades. It will doubtless be debated long after her death. What is safe to say is that she was a Janus-headed figure in women’s history, simultaneously progressive and retrogressive in her approach to women’s social roles.

Few magazines have been identified so closely with a single editor as Cosmopolitan was with Ms. Brown. Before she took over, Cosmopolitan, like its competitors, was every inch a postwar product. Its target reader was a married suburbanite, preoccupied with maintaining the perfect figure, raising the perfect child and making the perfect Jell-O salad.

Ms. Brown tossed the children and the Jell-O, though she kept the diet advice with a vengeance. Yes, readers would need to land Mr. Right someday — the magazine left little doubt that he was still every woman’s grail. But in an era in which an unmarried woman was called an old maid at 23, the new Cosmopolitan gave readers license not to settle for settling down with just anyone, and to enjoy the search with blissful abandon for however long it took. Sex as an end in itself was perfectly fine, the magazine assured them. As a means to an end — the right husband, the right career, the right designer labels — it was better still.

Gone was the housewife, apron in tow. In her place was That Cosmopolitan Girl, the idealized reader on whom Ms. Brown and her advertisers firmly trained their sights. Unencumbered by husband and children, the Cosmo Girl was self-made, sexual and supremely ambitious, a potent amalgam of Ragged Dick, Sammy Glick and Holly Golightly. She looked great, wore fabulous clothes and had an unabashedly good time when those clothes came off.

Forty-three when she took the magazine’s helm, Ms. Brown often described the Cosmo Girl as the young woman she had been — or dreamed of being — 20 years before.

A child of the Ozarks, Helen Marie Gurley was born on Feb. 18, 1922, in Green Forest, Ark., the younger of two daughters of a family of modest means. Her father, Ira, was a schoolteacher, as her mother, the former Cleo Sisco, had been before her marriage.

“I never liked the looks of the life that was programmed for me — ordinary, hillbilly and poor — and I repudiated it from the time I was 7 years old,” Ms. Brown wrote in her book “Having It All” (1982).

Photo

Ms. Brown in 1965.Credit
Sophia Smith Collection/Smith College

When Helen was a baby, Ira Gurley was elected to the state legislature, and the family moved to Little Rock. In 1932, when she was 10, Ira was killed in an elevator accident, leaving her mother depressed and impoverished. In 1937, Mrs. Gurley moved with her daughters to Los Angeles. There, Helen’s older sister, Mary, contracted polio; she spent the rest of her life paralyzed from the waist down and in later years battled alcoholism.

Though Helen was valedictorian of her high school class, she feared she could never transcend her family circumstances. At a time when a young woman’s main chance was to marry well, she felt ill equipped. She did not consider herself pretty, she wrote years afterward, and had rampant, intractable acne. She coined the word “mouseburger” to describe young women like her. [mouseburger, n., pejorative, < mouse + -burger. A physically unprepossessing woman with little money and few prospects. Cf. milquetoast, said of men.]

Helen Gurley persevered. She studied briefly at Texas State College for Women (it is now Texas Woman’s University), but with no money to continue, she returned to Los Angeles and enrolled in secretarial school, from which she graduated in 1941.

Around this time she had a short, inadvertent career as an escort. At 19, as Ms. Brown recounted in her memoir “I’m Wild Again” (2000), she answered a newspaper advertisement seeking young women for “social evenings.” She needed to support her mother and sister: What could be simpler, she reasoned, than earning $5 for going on a date? On her first outing, she and her gentleman caller parked and kissed a bit before the full extent of her responsibilities dawned on her. She fled with her $5 and her virtue.

She went on to hold a string of secretarial jobs — 17 by her own count — and discovered the measure of security that sex could bring. At every office, or so it seemed, there were bosses eager to fondle and dandle. In exchange, there might be a fur or an apartment or the wherewithal to keep her family going.

Helen Gurley eventually became an advertising copywriter in Los Angeles, first with Foote, Cone & Belding and later with Kenyon & Eckhardt. In 1959 she married David Brown, a former managing editor of Cosmopolitan who had become a Hollywood producer. “I look after him like a geisha girl,” she told The New York Times in 1970.

Mr. Brown, who produced “Jaws” and other well-known films, died in 2010; the couple had no children. Ms. Brown’s sister, Mary Gurley Alford, died before her.

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This year Ms. Brown gave $30 million to Columbia and Stanford Universities, both of which Mr. Brown had attended, to create the David and Helen Gurley Brown Institute for Media Innovation.

In the early 1960s, Ms. Brown found herself at loose ends and cast about for a project. Her husband, who had recently stumbled on a cache of letters she had written in her 20s to a married man who was smitten with her, persuaded her to write “Sex and the Single Girl.”

Though the book seems almost quaint today (“An affair can last from one night to forever”), it caused a sensation when it was published in 1962 by Bernard Geis Associates. It sold millions of copies, turned Ms. Brown into a household name and inspired a movie of the same title starring Natalie Wood, released in 1964.

In 1963, the Browns moved to New York. Two years later, the Hearst Corporation asked Ms. Brown to take over Cosmopolitan, one of its less prepossessing magazines. Becalmed in the doldrums, Cosmopolitan favored articles on home and hearth, along with uplifting discussions of current affairs (“The Lyndon Johnson Only His Family Knows”).

Ms. Brown had never held an editing job, but her influence on Cosmopolitan was swift and certain: she did not so much revamp the magazine as vamp it.

Where just months earlier Cosmo’s covers had featured photos of demure, high-collared girl-next-door types like Mary Tyler Moore, Ms. Brown’s first issue, July 1965, showed a voluptuous blond model whose deep cleavage was barely contained by her plunging neckline.

What Cosmopolitan’s previous cover lines had lacked in pith and punch (“Diabetes: Will Your Children Inherit It?”), Ms. Brown’s more than made up for. “World’s Greatest Lover — What it was like to be wooed by him!” her inaugural cover proclaimed. Ms. Brown was not shy about disclosing the fact that in her 32 years with the magazine, her husband wrote all the cover lines.

Readers and advertisers flocked to the new Cosmo. When Ms. Brown took over, the magazine had a circulation of less than 800,000; at its height, in the 1980s, circulation approached three million.

Ms. Brown’s magazine did not find favor with everyone. In 1970, a group of feminists led by Kate Millett staged a sit-in at Ms. Brown’s office, protesting what they saw as her retrograde vision of womanhood. Even several nude male centerfolds (Burt Reynolds, April 1972; Arnold Schwarzenegger, August 1977) were for many critics insufficient counterweights.

But in retrospect, Ms. Brown’s work seems strikingly apolitical, beholden mostly to the politics of personal advancement. (In “Having It All,” she compares herself, favorably, to Eva Peron.) The advice she offered Cosmopolitan’s readers on winning the right friends and influencing the right people was squarely in the tradition of Dale Carnegie, if less vertically inclined.

Ms. Brown was declared a living landmark by the New York Landmarks Conservancy, a private nonprofit organization, in 1995. Like many landmarks, she had much restoration work done, which she spoke of candidly: a nose job, breast augmentation, face-lifts, eye lifts and injections of silicone and fat into her face to keep wrinkles at bay, among other procedures.

But while she could offset the physical tolls of aging, Ms. Brown could not always keep pace with changing times. She drew wide criticism for publishing an article in the January 1988 issue of Cosmopolitan that played down the risk of AIDS for heterosexual women. In the 1990s, when prominent men like Justice Clarence Thomas and Senator Robert Packwood were facing accusations of sexual harassment, Ms. Brown publicly disdained the charges, arguing that sexual attention from men is almost always flattering. Her remarks angered many feminists.

In 1996, with circulation declining and the perception that Ms. Brown had lost touch with her readers growing, Hearst announced that she would step down the next year as editor in chief. Ms. Brown’s last issue was February 1997; she was succeeded by Bonnie Fuller, the founding editor of the American edition of Marie Claire magazine.

Ms. Brown stayed on as the editor of Cosmopolitan’s international editions, continuing to work from an office appointed with pink silk walls, leopard-print carpet and a cushion embroidered with the maxim “Good Girls Go to Heaven/Bad Girls Go Everywhere.”

Ms. Brown’s other books include “Sex and the Office” (1964), “Helen Gurley Brown’s Single Girl’s Cookbook” (1969) and “Sex and the New Single Girl” (1970), all published by Bernard Geis. In 1993, William Morrow published “The Late Show,” Ms. Brown’s advice book for women over 50, in which she suggests that as women age and the supply of available men dwindles, they should simply appropriate their friends’ husbands for jaunty recreational sex.

Perhaps none of these things — not the books, not the unabashed look of Cosmopolitan and its legion of imitators, not the giddy pleasure with which American women embraced sex without shame — would have happened quite as soon if Ms. Brown had heeded a single piece of advice. In 1962, just before “Sex and the Single Girl” was due to be published, she received a telegram from her mother. In an interview with CNN in 1998, Ms. Brown recalled its contents.

“dear helen,” it read. “if you move very quickly, i think we can stop publication of the book.”

Correction: August 16, 2012

An obituary on Tuesday about Helen Gurley Brown, the longtime editor of Cosmopolitan magazine, misstated part of the current name of the university in Texas that she attended. She briefly studied at Texas State College for Women, which is now known as Texas Woman’s University — not Texas Women’s University. The obituary also referred incorrectly to “mouseburger,” a word Ms. Brown invented to describe women, like her younger self, who were physically unprepossessing and had few prospects. She had used the word at least as early as 1971; she did not coin it in her book “Having It All,” published in 1982.

A version of this article appears in print on August 14, 2012, on Page A1 of the New York edition with the headline: Gave ‘Single Girl’ a Life in Full (Sex, Sex, Sex). Order Reprints|Today's Paper|Subscribe